The present invention relates generally to filters, and more particularly, to planar general response dual-mode cavity filters that may be used to produce microwave, high performance filters and multiplexers for satellite and wireless system applications.
Prior art generally relating to the present invention relates to cavity and single mode dielectric resonator filters, and includes the following:
U.S. Pat. No. 4,489,293 assigned to the assignee as the present invention, discloses a dual mode filter comprising several collinear dielectric loaded resonant cavities with their successive endwalls coupled. In the present invention, on the other hand, it is sufficient that the angle formed by the midpoints of any three proximate cavities is an integral multiple of 90xc2x0 and the sidewalls, not the endwalls, of the cavities are coupled. U.S. Pat. No. 4,489,293 uses iris or probe couplers between proximate cavities but does not suggest the use of a combined iris and probe coupling the same two cavities as in the present invention.
The device disclosed in U.S. Pat. No. 4,489,293 is mechanically difficult to mount and assemble, particularly in applications such as satellite transponders where complicated bracketing is necessary. Furthermore, the space between the cylindrically-shaped filter and surrounding planar equipment is not fully utilized. An optimum canonic filter realization for equal or greater than 6 poles requires an input and an output to be located in the same cavity; isolation between these two ports is difficult to achieve.
The present invention offers the following advantages. It is compatible with miniature MIC devices and is mechanically easier to mount. Integration with equalizers and isolators in the same housing is made possible. Because the cavities can follow a geometrically folded pattern, a realization of an optimum canonic response is easily achievable. Because of its larger heatsinking cross-section, the present invention has better heat transfer characteristics, especially in a vacuum environment. Therefore, application at higher power levels is possible.
U.S. Pat. No. 4,489,293 is elaborated upon in an article by S. J. Fiedziuszko and R. C. Chapman entitled xe2x80x9cMiniature Filters and Equalizers Utilizing Dual Mode Dielectric Resonator Loaded Cavitiesxe2x80x9d, 1982 International Microwave Symposium, IEEE MTT, Jun. 15-17, 1982.
U.S. Pat. No. 4,216,448 discloses an xe2x80x9cengine blockxe2x80x9d filter comprising several cavities. However, the patent uses a single coaxial TEM mode, and does not suggest the dual mode operation of the present invention. Dual mode operation allows the number of poles in the filter to be doubled because two modes resonate simultaneously within the same cavity, and one pole corresponds to each mode. This is very important in applications where weight and size are critical, such as in spacecraft. The filter of U.S. Pat. No. 4,216,448 is capable of coupling electrically adjacent modes only, not electrically nonadjacent modes as in the present invention. U.S. Pat. No. 4,216,448 does not suggest the use of dielectric resonators as in the present invention. The tuning screws of the filter of U.S. Pat. No. 4,216,448 protrude through the endwalls, not sidewalls as in the present invention. U.S. Pat. No. 4,216,448 does not suggest the use of a combined iris and probe coupler.
U.S. Pat. No. 4,135,133 discloses a collinear dual mode filter. It does not show combined iris/probe intercavity couplers. It does not show dielectric loading and does not show how one can geometrically fold the filter as in the present invention.
U.S. Pat. No. 4,267,537 discloses a circular TE0 mm mode sectorial filter, not a dual mode folded geometry cavity filter as is the present invention.
U.S. Pat. No. 3,516,030 discloses a hole in conjunction with a rod between two cavities and. The hole is not an iris because it does not interconnect the two cavities.
Other general references include U.S. Pat. Nos. 2,406,402, 3,475,642, and 3,680,012.
With regard to the most relevant prior art, U.S. Pat. 4,453,146 issued to Fiedziuszko and assigned to the assignee of the present invention, discloses an electromagnetic cavity filter is formed by at least two cavities having electrically conductive walls. When more than two cavities are employed, their midpoints do not have to be collinear; rather, it is sufficient that the angle formed by the midpoints of any three successively coupled cavities is an integral multiple of 90xc2x0. Thus, a folded xe2x80x9cengine blockxe2x80x9d geometry can be realized such that the filter""s input cavity is proximate to the output cavity. This allows a canonic filter response. Each cavity is the equivalent to two filter poles because two orthogonal modes of electromagnetic radiation can resonate therewithin. Electrically nonadjacent modes of proximate cavities, as well as electrically adjacent modes, can be coupled, permitting elliptic filter functions. Electrically nonadjacent modes are coupled by means of an iris opening between the two cavities. Electrically adjacent modes are coupled by means of an electrically conductive probe penetrating each of the two cavities. A dielectric resonator can be disposed within each cavity to reduce the physical size of the cavity while preserving its electrical characteristics.
While the filter disclosed in U.S. Pat. 4,453,146 was a significant improvements in the filter art, the present inventors have developed a more generalized filter than is disclosed in this patent that provides for variable input/output coupling and which is readily adaptable to many filter applications.
Accordingly, it would be advantageous to have improved planar general response dual-mode cavity filters. It would also be advantageous to have improved planar general response dual-mode dielectric loaded cavity filters.
The present invention provides for an improvement to the filter technology disclosed in U.S. Pat. 4,453,146, and provides for a planar general response dual-mode (dielectric loaded) cavity filter that is more adaptable than the filters disclosed in this patent. The present planar general response dual-mode cavity filter, which may be dielectrically loaded, enables realization of steeper response filters and asymmetric response filters in a dual mode filter configuration, which is not achievable using the technology disclosed in U.S. Pat. 4,453,146 or in other conventional filter designs. The present invention provides for the construction of improved microwave, high performance filters and multiplexers for use in satellite and wireless system applications.
The present invention provides for a device that filters electromagnetic radiation, comprising two or more resonant, generally cylindrical cavities. Angles connecting midpoints of any three proximate cavities can be any integral multiple of 90xc2x0, permitting a geometric folded, or block arrangement, in which the cavity accepting a filter input by way of an input element or input coupling apparatus is proximate to two other cavities, with one of the two other cavities generating a filter output by way of an output element or output coupling apparatus. Sidewalls of the cavities are intercoupled by means of probes and/or irises.
Resonating within each cavity can be two orthogonal degenerate modes of electromagnetic energy, i.e., HE111 waveoguide modes. Intercavity coupling is achieved by an iris, a probe, or a combination iris and probe coupling two adjacent cavities. Two electrically nonadjacent modes are coupled by an inductive iris. Two electrically adjacent modes are coupled by a capacitive probe. Each cavity may be loaded with a dielectric resonator to reduce the size and weight of the filter. Each cavity has characterizing vector tuning elements, which are typically tuning screws. Each cavity also has a mode coupling element, which also may be the form of a tuning screw. One cavity has an input element and a second cavity has an output element, which may be probes or irises.
Coupling irises or probes are selectively rotated at an angle with respect to a line through centers of adjacent intercoupled cavities. This rotation of the coupling irises or probes create additional mode couplings between the intercoupled cavities. The input and output elements may also be selectively rotated at an angle with respect to an axis that is perpendicular to a sidewall of each respective cavity. The input and output coupling apparatus or coupling elements may be disposed at locations that are angularly rotated with respect to the corresponding characterizing vector tuning element by a selectable angle that varies between 0 and xc2x1180 degrees.
The use of dual mode cavities allows for two filter poles per cavity. Compared with single mode filters, the present invention thus offers an approximate doubling in filter capability for the same weight and size.
The present invention offers mechanical mounting advantages compared with dual mode collinear filters, and can be readily integrated with other components, such as equalizers and isolators, in the same housing. Because of the geometrically folded, block design, a realization of optimum canonic response is easily achievable.